In recent years, an electrolyte membrane and an electrode for a polymer electrolyte fuel cell have been highly demanded. A dispersion composition of fluorine-containing ion exchange resin having a sulfonic acid functional group (hereinafter simply referred to as a “fluorine-containing ion exchange resin” at times) has been used for the production or repairing of electrolyte membranes for polymer electrolyte fuel cells, the production of electrodes containing catalyst particles, and the like.
A dispersion composition of ion exchange resin has been required to have low viscosity in a higher concentration, so that it can be an easy-to-use material for electrolyte membranes and electrodes.
Typical examples of a dispersion composition of fluorine-containing ion exchange resin having a sulfonic acid functional group include Nafion® Dispersion Solution (manufactured by DuPont, U.S.A.) and Aciplex®-SS (manufactured by Asahi Kasei Chemicals Corporation). Since the dispersibility of such fluorine-containing ion exchange resin having a sulfonic acid functional group in a solvent is extremely low, dispersion compositions produced by dispersing fluorine-containing ion exchange resins in solvents according to various techniques have been proposed, so far.
For example, Patent Document 1 discloses a solution of a sulfonic acid-containing fluorocarbon polymer in alcohol.
In addition, Patent Document 2 discloses a liquid composition of perfluoro ion exchange polymer having an equivalent weight of from 1025 to 1500.
Moreover, Patent Document 3 discloses a highly fluorinated ion exchange polymer particle-containing composition, which has been subjected to a dispersion treatment using a dispersion medium containing water, or water and benzene.
Patent Document 4 discloses a dispersion liquid of a sulfonic acid perfluoro copolymer produced by a homogenization method using a disperser, and Patent Document 5 discloses a dispersion liquid of a sulfonic acid perfluoro copolymer, which is produced by a method comprising performing a washing step in water under heating/pressurizing conditions, and then performing a dispersion treatment.    [Patent Document 1] Japanese Patent Publication No. 48-13333    [Patent Document 2] Japanese Patent Laid-Open No. 57-192464    [Patent Document 3] Published Japanese translations of PCT International publication No. 2001-504872    [Patent Document 4] Japanese Patent Laid-Open No. 2005-82749    [Patent Document 5] Japanese Patent Laid-Open No. 2005-82748